The field of the invention is in the art of measuring nondestructively the permeability and resistivity of metal sheets.
Many buildings use steel as a magnetic shielding material. The magnetic properties of the steel are an important parameter in determining the quality of the shield. Frequently it is desired to use a previously constructed steel structure as a magnetically shielded enclosure and data on the material used is not available. Also, it is desirable to verify the shielding capabilities of newly constructed structures. The usual technique is to take a sample, i.e., cut it out of the existing structure, and run a B-H curve of the sample. This impairs the shield and frequently the properties of the sample are altered in the removing process and the measurements obtained therefrom are not truly indicative of the sheet from which it was removed.
Typical examples of the current state of the art are exemplified by U.S. Pat. Nos. 2,659,857 to patentee C. A. Anderson; 2,828,467 to patentee L. H. Stauffer; 3,611,125 to patentees Meyer Press et al; and 3,646,436 to patentees J. Y. Chan et al.